think of whatever is AFTER the trellis encoder and BEFORE the viterbi
decoder as an equivalent channel.
What is the equivalent channel in your case?
What is its input alphabet? what is its output alphabet?
From your description, it seems that the input alphabet is the same as
the output alphabet of your FSM.
I am not familiar with the block “packet decoder” so i don’t know what
it outputs, but whatever it is it should be the output alphabet of your
Once you figure out these things it will be straightforward to see what
the viterbi block should be…
If you gather these pieces of information and still don’t see how to
implement the viterbi decoder let me know and i will provide further